From 5d4861867adc86776f6674f1bf0d6e1891119d68 Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Mon, 17 Jun 2013 21:45:18 +0000
Subject: [PATCH] MI-Sched: handle ReadAdvance latencies as used by Swift.

llvm-svn: 184135
---
 llvm/lib/CodeGen/TargetSchedule.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/TargetSchedule.cpp b/llvm/lib/CodeGen/TargetSchedule.cpp
index 53cd11c5daa6..64ee9d1c464e 100644
--- a/llvm/lib/CodeGen/TargetSchedule.cpp
+++ b/llvm/lib/CodeGen/TargetSchedule.cpp
@@ -201,7 +201,10 @@ unsigned TargetSchedModel::computeOperandLatency(
     if (UseDesc->NumReadAdvanceEntries == 0)
       return Latency;
     unsigned UseIdx = findUseIdx(UseMI, UseOperIdx);
-    return Latency - STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
+    int Advance = STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
+    if (Advance > 0 && (unsigned)Advance > Latency) // unsigned wrap
+      return 0;
+    return Latency - Advance;
   }
   // If DefIdx does not exist in the model (e.g. implicit defs), then return
   // unit latency (defaultDefLatency may be too conservative).